The final words that Star Wars film were taken as a direct threat by the Dark Lord of the Sith. Every fan re the moment that the former Anakin Skywalker struck down his Jedi master at the end of A New Hope. The seasoned Jedi tells Vader, "If you strike me down, I'll become more powerful than you can possibly imagine." As the story continues, it becomes apparent that Obi-Wan meant that his death would inspire Luke to topple the Sith, but to Vader, his words were perceived a lot differently.
In Marvel's current run of Star Wars comics, Darth Vader believes that Obi-Wan's final words are nothing more than "Jedi tricks," but he eventually comes to realize their true meaning. However, one Legends-era comic perfectly highlights why these words might haunt Vader. While the Jedi tend to interpret words and messages from "a certain point of view," the Sith take warnings like these much more literally.
The 2003 anthology comic Star Wars Tales #16 features a story "Heart of Darkness," written by Paul Lee with art by Paul Lee and Brian Horton. This story explains why Kenobi's threat was the perfect thing to level against Darth Vader. While it is a Legends story that is no longer canon, many of its themes and ideas do hold up in the current canon. The story centers around a young Jedi of Yoda's species named Minch, who travels to Dagobah where he meets and battles a dark Jedi. The dark Jedi makes the same threat to Minch, and he means it very literally. When Minch strikes him down, the dark Jedi splits into dozens of tiny versions of himself and quickly overtakes his opponent. He takes the threat a step further by claiming that he will show Minch what true power is.
Understanding the Sith's focus on the individual versus the Jedi's focus on the collective also helps drive this point home. The Jedi seek to become one with the Force after death, whereas the Sith strive to maintain the self and stay in the physical realm as long as possible. With this in mind, it's understandable why a Sith adherent like Vader would misinterpret Kenobi's words as a literal threat. The moment he strikes his former master down, he expects an immediate reaction, and when nothing happens, he takes it to mean that the Jedi's Force power has failed to manifest.
Not only is this a genius move on Obi-Wan's part, but it is also a great way to showcase what makes the Jedi different from the Sith. This is Obi-Wan Kenobi's final lesson to Darth Vader, who grows to understand what it means as the rest of the Star Wars saga unfolds.
